(a) Field of the Invention
The present invention relates to an electronic ballast. More specifically, the present invention relates to an electronic ballast that has a small number of components and a high degree of efficiency.
(b) Description of the Related Art
An electronic ballast provides stable power to lighting apparatuses such as fluorescent lamps and discharge tubes.
Since the fluorescent lamp and discharge tube emit light via a discharge process, the polarity of the supplied power must be switched at predetermined periods. To supply such power, the electronic ballast is implemented with a converter. Typically, a boost converter, half bridge converter, and flyback converter are used.
A conventional electronic ballast will now be described with reference to the drawings.
Referring to FIG. 1, the conventional electronic ballast using the boost converter and half bridge converter comprises a rectifier 10, a boost converter 20, a diode D1, a capacitor C1, a half bridge converter 30, a resonance circuit 40, and a lamp Rlamp.
The rectifier 10 receives, rectifies, and outputs an alternating current (AC).
The boost converter 20 comprises a coil L1 and a switch S1, and receives the rectified power to boost the power to a predetermined level, after which the boost converter 200 outputs the result.
One end of the diode D1 is coupled to the coil L1 and the switch S1 and its other end is coupled to one end of the capacitor C1, the other end of the capacitor C1 being grounded. The diode D1 and capacitor C1 smooth the output of the boost converter 20.
The half bridge converter 30 is coupled to both ends of the capacitor C1 and comprises two switches S2 and S3. The half bridge converter 30 changes the polarities of the power by performing the switching operation on the voltage at the capacitor C1 at a predetermined period, and outputs the result so that AC power is supplied to the discharge tube.
The resonance circuit 40 comprises capacitors C2 and C3 and a coil L2, and resonates the output power of the half bridge converter 30 to convert the output power to AC power having a predetermined frequency. After this conversion, the resonance circuit 40 supplies the AC power to the lamp Rlamp.
As shown in FIG. 2, the electronic ballast using the conventional flyback converter and half bridge converter comprises a rectifier 10, a flyback converter 50, a diode D1, a capacitor C1, a half bridge converter 30, a resonance circuit 40, and a lamp Rlamp.
The flyback converter 50, by the on and off operation of a switch S1, receives an output power of the rectifier 10 from a primary coil of a transformer T1, performs conversion of the power, then transmits the result to a secondary coil of the transformer T1.
In the above-noted conventional electronic ballast, a system having a boost converter connected to a half bridge converter, and another system having a flyback converter connected to a half bridge converter are described. The overall performance of such systems decreases as a result of these inefficient interconnections. Also, since the elements are physically coupled, the size of the circuit increases with an increase in the number of components, and overall reliability decreases. Manufacturing costs also go up with such configurations.